Re: Need some advice on water cooling
Definitely get the 5870 if you're concerned about heat! The HD5000 series are very power efficient GPU's. They'll still dump out a ton of heat but it is much less than two GTX470's will put out. One 5870 will run pretty much anything at high to full settings on a single monitor. It will also run most games (all but the hardest such as Crysis) across up to 3 monitors in Eyefinity at high settings (everything but Anti Aliasing). Two 5870's will outperform two GTX470's while running cooler and the stock 5870 heatsink/fan is very good on the reference design cards.
nVidia's GTX4 lineup is generally more power hungry and hotter running than previous cards from either side so I would not recommend them for a hot room.
As for the 5870, it OC's very well, pushed mine up 100MHz core, 100MHz memory (as far as ATi Overdrive will allow) with no problem and barely any temperature change. I had to set the fan up to 50% but with a water cooler it shouldn't be an issue. I stay under 70C (in a cool room under 60C) while gaming at that fan speed which is good for a long lasting setup. The HD5870 (standard edition, not Eyefinity 6 Edition) can drive up to 3 monitors though you will need a DisplayPort monitor or active adapter for the third. With 2 DVI cables and a DP-VGA adapter I am running 3 1920x1080 monitors off one 5870 and it works very well. They can be configured as split monitors for multitasking or grouped into one large monitor for gaming and switching between setups is easy.